1. Field
The present invention relates to an inorganic semiconductor light emitting device, and more particularly, to a near ultraviolet light emitting device.
2. Discussion of the Background
Generally, a gallium nitride-based semiconductor has been widely used in a blue/green light emitting diode or a laser diode as a light source of full color displays, traffic lighting, general lamps and optical communication instruments. In particular, an indium gallium nitride (InGaN) compound semiconductor has attracted considerable attention due to its narrow band gap.
This gallium nitride-based compound semiconductor has been utilized in various fields such as large-sized natural color flat panel display devices, light sources of backlight units, traffic lights, indoor lighting fixtures, high density light sources, high resolution output systems, optical communication, and the like. A light emitting device for emitting near ultraviolet light has been used in forgery discrimination, resin curing and ultraviolet treatment, and can realize various colors of visible light in combination with a fluorescent substance.
Near ultraviolet light refers to ultraviolet light at wavelengths ranging from about 320 nm to 390 nm. Gallium nitride GaN has an energy band gap of about 3.42 eV, which correspond to optical energy at a wavelength of about 365 nm. Accordingly, a light emitting device including an InGaN well layer can be used to emit near ultraviolet light at wavelengths of 365 nm or greater, that is, wavelengths from 365 nm to 390 nm according to In content.
Since light produced in the well layer is emitted to the outside through a barrier layer and a contact layer, a plurality of semiconductor layers is located in a path along which light travels, and light absorption occurs due to the semiconductor layers. In particular, when the semiconductor layers have a band gap smaller than or similar to those of the well layers, significant light loss occurs. In particular, it is necessary to control light absorption due to an n-type contact layer and a p-type contact layer occupying most of the thickness of the light emitting device.
Thus, in the near ultraviolet light emitting device in the related art, barrier layers, n-type contact layers, and p-type contact layers as well as electron blocking layers are formed of AlGaN which has a greater band gap than InGaN. However, since it is difficult to grow AlGaN relatively thick while ensuring good crystallinity of AlGaN, electric and optical characteristics of the near ultraviolet light emitting device are inferior to those of blue light emitting devices, and the near ultraviolet light emitting device is sold at a higher price than blue/green light emitting devices.